| 1. |
E. D.P. Perera, K. Jinno, A. Tsutsumi, Y. Hiroshiro, Three dimensional solute transport numerical modeling of salinity fluctuations in a coastal aquifer, 18th World IMACS Congress and International Congress on Modelling and Simulation: Interfacing Modelling and Simulation with Mathematical and Computational Sciences, MODSIM 2009, 2020, Over-exploitation of groundwater in coastal aquifers is one of the major reasons for saltwater intrusion. Saltwater intrusion contaminates the freshwater resource in coastal aquifers by increasing the salinity levels of the groundwater. A small quantity of saltwater is enough to contaminate the large quantity of freshwater in a coastal aquifer. Therefore, saltwater intrusion should be considered seriously. Numerical models are needed to enhance the understanding of saltwater intrusion and its related phenomena extensively. The Motooka region in the Fukuoka prefecture in Japan is a coastal area, where groundwater is the main water resource for green house agriculture and domestic use. Over-exploitation of groundwater in this coastal region has resulted in saltwater intrusion and thus in the contamination of the freshwater aquifer. In addition to the more obvious effects of saltwater intrusion, fluctuations in salinity caused by such intrusion is a crucial problem to address, since even slight changes in salinity of the water use for agricultural purposes significantly affect the crop's growth and yield. So far, a research on the salinity fluctuations with groundwater pumping and their effects on seasonal recharge of groundwater in the Motooka region has not been conducted. Therefore, in this study a three-dimensional density-dependent solute transport flow model is developed to simulate the salinity fluctuations due to groundwater pumping. In the present numerical study, the emphasis is on the development of conceptual, mathematical and numerical model of variable density flow and solute transport and its application to simulate the salinity fluctuation due to groundwater pumping at different rates. The model is based on the “transition zone” approach, which considers the interface as a miscible zone where freshwater and saltwater is mixing while maintaining a density gradient across the freshwater/saltwater interface. The transition zone approach requires simultaneous solutions of the governing water flow and solute transport equations. To this end, the model incorporates three fundamental equations in flow and solute transport, namely Darcy's law, general groundwater flow equation and the advection dispersion solute transport equation. The groundwater flow equation and solute transport equation are coupled by the equation of state to produce the salt concentration at each time step for whole flow domain. The finite difference method is used as the numerical technique to solve the partial differential equations of flow and transport under an implicit scheme. The method of characteristics is applied to solve the advection term in the solute transport equation. A non-uniform discretized grid system is adopted in the flow domain allocating relatively small grid sizes to pumping well locations. To achieve reliable results, relevant and important hydro-geological parameters are assigned to the numerical model after considering the hydrological situation of the Motooka region. Different boundary conditions are assigned considering the dominant hydrological processes those are believed to be in effect in the selected area. The numerical results obtained from the model demonstrate the salinity variation due to groundwater pumping and seasonal recharge rates from year 2001 to 2007 under the influence of saltwater intrusion. The results also reveal that model is capable of correctly simulating the physical processes. A comparison of the measured and modeled electric conductivities shows reasonable agreement.. |
| 2. |
広城 吉成, 小西 啓介, 寺嶋 健人, 堤 敦, Quantitative Analysis of Nutrient Inflow from River and Groundwater to Imazu Bay in Fukuoka, Japan, ICEWRM 2016:18th International Conference on Environment and Water Resource Management, 2016.05, Imazu Bay plays an important role for endangered species such as horseshoe crabs and black-faced spoonbills that stay in the bay for spawning or passing the winter. However, this bay is semi-enclosed with slow water exchange, which could lead to eutrophication under the condition of excess nutrient inflow to the bay. Therefore, quantification of nutrient inflow is of great importance. Generally, analysis of nutrient inflow to bays takes into consideration nutrient inflow from only river, but that from groundwater should not be ignored for more accurate results.
The main objective of this study is to estimate amounts of nutrient inflow from river and groundwater to Imazu Bay by analyzing water budget in Zuibaiji River Basin and loads of T-N, T-P, NO3-N and NH4-N. The water budget computation in the basin is performed using groundwater recharge model and quasi three-dimensional two-phase groundwater flow model, and the multiplication of the measured amount of nutrient inflow with the computed discharge gives the total amount of nutrient inflow to the bay. In addition, in order to evaluate nutrient inflow to the bay, the result is compared with nutrient inflow from geologically similar river basins.
The result shows that the discharge is 3.50×107 m3/year from the river and 1.04×107 m3/year from groundwater. The submarine groundwater discharge accounts for approximately 23% of the total discharge, which is large compared to the other river basins. It is also revealed that the total nutrient inflow is not particularly large. The sum of NO3-N and NH4-N loadings from groundwater is less than 10% of that from the river because of denitrification in groundwater. Shin Seibu Sewage Treatment Plant located below the observation points discharges treated water of 15,400 m3/day and plans to increase it. However, the loads of T-N and T-P from the treatment plant are 3.9 mg/L and 0.19 mg/L, so that it does not contribute a lot to eutrophication.
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| 3. |
E. D.P. Perera, K. Jinno, Yoshinari Hiroshiro, A. Tsutsumi, Evaluation of seawater intrusion to a coastal aquifer by developing a three dimensional numerical model, International Conference on Hydrological Changes and Management from Headwaters to the Ocean, HYDROCHANGE 2008, 2009.12, The Motooka region in Fukuoka, Japan is a coastal region where agriculture is dominant. The green houses and wineries cover their water demand from groundwater. With the increased water demand, seawater intrusion is identified as an alarming threat to the Motooka coastal aquifer in near future. The measured electric conductivities of the water samples have been analyzed periodically. Until now the measured electric conductivities do not show high values but those values convince the emerging threat of seawater intrusion in this aquifer in future if groundwater will be pumped at current rate further. Therefore it is worth to conduct a numerical study of seawater intrusion and its impact to the Motooka area since the sustainability of the aquifer is inevitable for the future groundwater development and agriculture. In this paper a numerical study of the seawater intrusion of the Motooka is discussed. The numerical model presented in this paper was developed by coupling the groundwater flow equation with the mass transport equation to simulate the density dependent solute transport in the three dimensional space. The usage of this model as a management tool to simulate the salinity variation with groundwater pumping is emphasized. The numerical model was adequately capable of simulating the seawater intrusion and numerical results show a satisfactory agreement with the field observations.. |
| 4. |
E. D.P. Perera, K. Jinno, A. Tsutsumi, Y. Hiroshiro, Three dimensional solute transport numerical modeling of salinity fluctuations in a coastal aquifer, 18th World IMACS Congress and International Congress on Modelling and Simulation: Interfacing Modelling and Simulation with Mathematical and Computational Sciences, MODSIM09, 2009.12, Over-exploitation of groundwater in coastal aquifers is one of the major reasons for saltwater intrusion. Saltwater intrusion contaminates the freshwater resource in coastal aquifers by increasing the salinity levels of the groundwater. A small quantity of saltwater is enough to contaminate the large quantity of freshwater in a coastal aquifer. Therefore, saltwater intrusion should be considered seriously. Numerical models are needed to enhance the understanding of saltwater intrusion and its related phenomena extensively. The Motooka region in the Fukuoka prefecture in Japan is a coastal area, where groundwater is the main water resource for green house agriculture and domestic use. Over-exploitation of groundwater in this coastal region has resulted in saltwater intrusion and thus in the contamination of the freshwater aquifer. In addition to the more obvious effects of saltwater intrusion, fluctuations in salinity caused by such intrusion is a crucial problem to address, since even slight changes in salinity of the water use for agricultural purposes significantly affect the crop's growth and yield. So far, a research on the salinity fluctuations with groundwater pumping and their effects on seasonal recharge of groundwater in the Motooka region has not been conducted. Therefore, in this study a three-dimensional density-dependent solute transport flow model is developed to simulate the salinity fluctuations due to groundwater pumping. In the present numerical study, the emphasis is on the development of conceptual, mathematical and numerical model of variable density flow and solute transport and its application to simulate the salinity fluctuation due to groundwater pumping at different rates. The model is based on the "transition zone"approach, which considers the interface as a miscible zone where freshwater and saltwater is mixing while maintaining a density gradient across the freshwater/saltwater interface. The transition zone approach requires simultaneous solutions of the governing water flow and solute transport equations. To this end, the model incorporates three fundamental equations in flow and solute transport, namely Darcy's law, general groundwater flow equation and the advection dispersion solute transport equation. The groundwater flow equation and solute transport equation are coupled by the equation of state to produce the salt concentration at each time step for whole flow domain. The finite difference method is used as the numerical technique to solve the partial differential equations of flow and transport under an implicit scheme. The method of characteristics is applied to solve the advection term in the solute transport equation. A non-uniform discretized grid system is adopted in the flow domain allocating relatively small grid sizes to pumping well locations. To achieve reliable results, relevant and important hydro-geological parameters are assigned to the numerical model after considering the hydrological situation of the Motooka region. Different boundary conditions are assigned considering the dominant hydrological processes those are believed to be in effect in the selected area. The numerical results obtained from the model demonstrate the salinity variation due to groundwater pumping and seasonal recharge rates from year 2001 to 2007 under the influence of saltwater intrusion. The results also reveal that model is capable of correctly simulating the physical processes. A comparison of the measured and modeled electric conductivities shows reasonable agreement.. |
| 5. |
M. Katsuki, J. Yasumoto, A. Tsutsumi, Yoshinari Hiroshiro, K. Jinno, Estimation of groundwater discharge to the sea using a distributed recharge model, International Conference on Hydrological Changes and Management from Headwaters to the Ocean, HYDROCHANGE 2008, 2009, Groundwater discharge to sea areas affects environmental conditions along coasts. Enclosed bays may experience eutrophication caused by nutrient input from land areas through groundwater discharge since groundwater is often contaminated by large amounts of nutrients as compared with river water. Therefore, it is necessary to estimate the groundwater discharge into seas quantitatively in order to understand nutrient pathways. A distributed groundwater recharge model was developed in order to estimate total groundwater discharge flow into the Ariake Bay, in Kyushu, Japan. The Komoda catchment within the Kikuchi River basin in Kumamoto prefecture was studied as a representative area for the Ariake Bay. The model partitions rainfall into direct runoff, evapotranspiration, and groundwater recharge. Parameters are set based on land use. Groundwater discharge is calculated using a water balance approach. The results show that groundwater discharge into the Ariake Bay from Kukuchi River basin is on average 123 mm year-1. The groundwater discharge accounts for about 8% of total water discharge and 9% of river discharge. The results can be used to better estimate annual transport of nutrients in the groundwater to the sea and thus also to better manage eutrophication problems.. |
| 6. |
K. Jinno, T. Hosokawa, K. Akagi, Y. Hiroshiro, J. Yasumoto, Geochemical processes and their modelling at the fresh and salt water mixing zone, International Conference on Calibration and Reliability in Groundwater Modelling: Credibility of Modelling, ModelCARE2007, 2008.11, Oxidation-reduction geochemical processes coupled with mass transport in a coastal aquifer is a unique subsurface environmental phenomenon to model. When a porous material is contaminated by organic carbons, nitrate is denitrified and manganese dioxide and oxi-iron hydroxide would be reduced. However, it is expected that the reduced divalent iron is oxidized once again by seawater when discharged to the sea. The paper discusses a numerical model of transport and geochemical reaction processes along the mixing zone of fresh and reduced salt water in a coastal aquifer. By comparing the numerical solution with experimental observations for the precipitation of divalent iron along the mixing zone, the validity of the model is demonstrated.. |
| 7. |
Abdul Halim, Kenji Jinno, Abdur Razzak, Keita Oda, Yoshinari Hiroshiro, Experimental and biogeochemical modeling studies on arsenic release in soil under anaerobic condition, 23rd Annual International Conference on Soils Sediments and Water 2007, 2007, The identification of release mechanisms of arsenic may assist in designing safe and effective remediation strategies, due to its severe toxicity effect for the human body. In this regards, investigations were carried out to observe the release of As from soil into water. It was found that As concentration increased with decreasing oxidation reduction potential. Arsenic concentrations demonstrated negative covariation with the concentrations of NO3 but strongly correlated with DOC and Fe concentrations. Batch leaching tests at different pH conditions showed a strong pH dependence on arsenic and iron leaching. A numerical simulation of arsenic transport model, coupled with microbially mediated biogeochemical processes was developed for describing the release of As in soil under reducing environment. The simulation concentrations of Mn, Fe and As were well matched those found experimentally. The results of this study suggested that the microbially mediated degradation of organic matter and reductive dissolution of Fe-oxyhydroxide are considered to be the dominant processes to release As in aquifers.. |
| 8. |
Jun Yasumoto, Mamoru Katsuki, Hidetomo Takaoka, Yoshinari Hiroshiro, Kenji Jinno, Nutrient inputs through submarine groundwater discharge to Ariake Bay, Kyushu Island, Japan, International Symposium: A New Focus on Groundwater - Seawater Interactions - 24th General Assembly of the International Union of Geodesy and Geophysics (IUGG), 2007, Submarine groundwater discharge (SGD) is now recognized as an important pathway between land and sea. This study attempts to estimate the nutrient inputs through SGD to Ariake Bay. SGD rates and its quality along the coast of Ariake Bay in the Oura Region, Japan, were investigated. It was shown that the on-site SGD rate ranges from 0.01 to 20.52 μm/s, and SGD flows through the shallow confined aquifers, which consist of two kinds of rocks: basalt and pyroclastic rocks. The reduction reaction for SGD proceeded just up to denitrification. SGD associated with nutrient loads of N, P and SiO2 were estimated to be 1.40, 0.07 and 52.78 g m-2 d-1, respectively. This study demonstrates that SGD must be considered as a significant source of nutrient input to the coastal sea area in Ariake Bay.. |
| 9. |
E. D.P. Perera, K. Jinno, A. Tsutsumi, Y. Hiroshiro, Simulation of saltwater intrusion caused electric conductivity fluctuations due to groundwater pumping in a coastal aquifer, International Congress on Modelling and Simulation - Land, Water and Environmental Management: Integrated Systems for Sustainability, MODSIM07, 2007. |
| 10. |
Y. Hiroshiro, K. Jinno, S. I. Wada, T. Yokoyama, M. Kubota, Multicomponent solute transport model with cation exchange in a redox subsurface environment, ModelCARE'99 Conference, 2000.01, In order to clarify the behaviour of chemical species under reducing condition in a subaqueous soil similar to a paddy field, a column experiment was carried out. As Mn- and Fe-(hydr)oxides were dissolved by microbially mediated reduction, Na+, K+, Mg2+, Ca2+, Mn2+, and Fe2+ existed in the pore water as major cations. The Ca2+ concentration had a tendency to decrease in the layer at 5-25 cm depth in the column, whereas the Ca2+ concentration increased with time below 45 cm depth. This phenomenon can be assumed to be due to the desorption of Ca2+, by Mn2+ and Fe2+, and its infiltration. Therefore, it is necessary to develop a solute transport model which takes into account both biochemical and cation exchange reactions. In this paper, a simulation model that considers both reactions is described and applied to simulate the results of the column experiment. The reliability of this model was evaluated by comparing the calculated results with the result of the experiment.. |
